The present invention relates to a power management system for an energy storage system.
With the high levels of penetrations of renewable energy resources in power grid, e.g. Photovoltaic (PV), the system encounters many challenges, e.g. power quality, voltage fluctuations, etc. One of the concerns comes from the short-term high-frequency variations of the PV generation during unpredictable sudden weather changes, which has been reported at some central generation stations. A great effort has been put in the mitigation of the short-term fluctuation of PV power generation, which is generally called as smoothing or ramp-rate control. The effective solution is to add energy storage device for PV integration.
The batteries, as the most common energy storage devices, have high energy density, but relatively low power density. Usually the PV power output smoothing requires frequent and high charging/discharging power from storage devices, which will greatly shorten the battery life. So the hybrid energy storage system is introduced to effectively utilize the characteristic of different storage devices. For example, the ultracapacitor (UC), featured with high power density and relatively low energy density, can compensate battery system and alleviate the high power pressure on battery system. However considering the expensive cost of these energy storage devices, the optimal power management strategy is necessary for the optimal use of these energy storage devices for certain system applications.